Arbitrarily polarized slot antenna



Feb. 20, 1962 F. J. GOEBELS, JR., ETAL 3,022,506

ARBITRARILY POLARIZED SLOT ANTENNA Filed March 27, 1959 e Sheets-Sheet 1IIIVAMW Mia/V5405 fizz/Ja uar J2, 1214 1 a (44 )6 (law Feb. 20, 1962 F.J. GOEBELS, JR., ETAL 3,

ARBITRARILY POLARIZED SLOT ANTENNA 6 Sheets-Sheet 2 Filed March 27, 1959Feb. 20, 1962 F. J. GOEBELS, JR, ETAL ARBITRARILY POLARIZED SLOT ANTENNA6 Sheets-Sheet 3 Filed March 27, 1959 flaw/M7 7 241 Zia-5a: die, lam 746. 624

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Feb. 20, 1962 F. J. GOEBELS, JR., ETAL 3,022,505

ARBITRARILY POLARIZED SLOT ANTENNA Filed March 27, 1959 6 Sheets-Sheet 4Feb. 20, 1962 F. J GOEBELS, JR., ETAL 3,022,506

ARBITRARILY POLARIZED SLOT ANTENNA Filed March 27, 1959 6 Sheets-Sheet 5Feb. 20, 1962 F. J. GOEBELS, JR., ETAL 3,022,505

ARBITRARILY POLARIZED SLOT ANTENNA 6 Sheets-Sheet 6 Filed March 27, 1959W I V MM i; M... in w. A Z M I Z W! Z w a m 4 a g! n .llllllll-IIIIXVIII/41f. iv :Zfazaazriz, AVI/VVFAJ. A470,

lime/AX United States This invention relates to antennas, andparticularly to microwave antennas capable of transmitting and receivingradiation of any polarization and having a planar surface.

No matter what the environment in which an antenna is to be used, it isalways, of course, desirable to employ a design which is simplyconstructed and which has small size and weight. It is recognized thatin the antenna art complex functions can be provided by using large andcomplicated structures, each part of which performs at least a part ofthe desired functions, In many situations, however, the complexstructures cannot be practicably used. Thus in an aircraft a large andheavy antenna may impose weight penalties which limit the use of theaircraft. It is particularly desirable that antennas for use with highspeed vehicles be small in size and light in weight, and it is furtherhighly desirable to have antennas which can be mounted flush with astreamlined surface. For this reason, a planar or level antenna whichcan be mounted flush with an aircraft surface has particular utility. itWill be recognized that if such an antenna has little weight and is ofsmall size it will be of especial benefit.

in many cases, the characteristics of operation of an antenna may bemore important than the structural features and the configuration of thedevice. There is a widespread need for antennas Whose responsiveness andoperation is independent of the polarization which they radiate orreceive. In radar and in other arts which utilize radiation echoes, forexample, it is often found that returned waves do not correspond inpolarization to the radiated waves. The polarization of the receivedwave is affect-ed both by the polarization of the transmitted radiationand by the nature of the object from which it is reflected.Consequently, if an antenna is employed which is sensitive to only onedirection of polarization, (e.g. vertical polarization), as manyantennas are, the system reception is greatly lessened, and may besubject to excessive error signal components. If, however, an antenna isemployed which can operate with any linear polar zation, with circularpolarization in either sense of rotation, or with ellipticalpolarization, optimum polarizaiton detection will always exist. Antennaswhich display this polarization versatility are usually calledarbitrarily polarized antennas. Such an antenna can provide a number ofadvantages for the system with which it is employed. For example,changes in the polarization of the radiation can be made to achieveoptimum response from an obected having given characteristics.Furthermore, its inherent omnipolarization capabilities can improve thesystem response to received signals. In addition, the ability to changethe polarization makes possible a more detailed analysis of the natureof objects from which energy is reflected, due to the fact that variousobjects have different characteristic effects upon the polarization ofthe radiation which they reflect.

The combination of these electrical characteristics and operativefeatures with desirable mechanical features has in the past beenextremely dificult. The use of an antenna having arbitrary polarizationcapability but which is small in size is difiicult enough, but theproblems are compounded when it is additionally required that theantenna be fed simply and also be of a streamlined configuration. It isfurther desirable that the antenna be atent C) 31,022,596 Patented Feb.20., 1952 easily fabricated, and if possible that the antenna use aplanar radiating surface so as to avoid the necessity for an extensivefront feeding structure. Such an antenna can operate effectively withoutneed for a radome, but still can provide a two-dimensional, as opposedto a linear, array.

It is therefore an object of the present invention to provide atwo-dimensional, planar antenna having arbitrary polarizationcapability.

Yet another object of the present invention is to provide novel antennaforms which may be simply constructed and which can provide selectedlinear, circular or elliptical polarization.

Yet another object of this invention is to provide lightweight antennastructures capable of generating a pencil beam from a planar surfacewhich can be flush mounted with a supporting body.

Yet another object of this invention is to provide an improved planarantenna for mobile applications Whose pattern response remains invariantwith the polarization of operation.

It is a further object of this invention to provide a smalltwo-dimensional microwave antenna which can be simply constructed andwhich operates to provide ready control of the antennas polarization.

Yet another object of this invention is to provide an improved antennacapable of arbitrarily changing the polarization characteristics ofradiated energy.

A further object of this invention is to provide a simply fed andconstructed compact antenna capable of being flush mounted in astreamlined structure and suitable for providing selective polarizationcontrol.

It is yet another object of this invention to provide an improvedantenna for providing a broadside pencil beam pattern from atwo-dimensional surface.

A further object of this invention is to provide a planar antennacapable of producing an angularly symmetric pattern independent of thepolarization which is radiated or received.

Yet another object of this invention is to provide an improved planarantenna capable of conical scanning.

These and other objects of this invention are achieved by an arrangementin accordance with the invention which utilizes a radial wave guide andwhich also employs a v composite radiating aperture consisting of atleast one annular slot defined by a number of individual elements livingin a circlt concentric with the central axis of the radial Waveguide.configuration, such as a crossed slot, which can be excited in anydirection in the plane in which they lie. In one form of the invention,the antenna aperture thus defined is excited in a standing wave mode sothat each of the crossed slots is excited so as to provide likepolarized radiation. This arrangement may use a circular waveguide whichis coupled to the radial Waveguide at its central axis and which isexcited in its dominant TE mode to provide excitation of the radialwaveguide in the E mode. The E radial wave guide mode establishes radialand circumferential currents at the annular slots having like amplitudesbut a ninety degree electrical separation. The radial andcircumferential attitudm of the crossed slot elements, plus the excitingcurrents cause the resultant component of the radiation vector at eachslot to be equal in magnitude and to lie parallel to the same plane ofpolarization for any polarization at any given instant of time. Thedirection of polarization is controlled by the polarization of the TEfeed mode. With this arrangement, circularly polarized energy may beprovided by establishing orthogonally disposed feed modes which excitethe crossed slots equally in amplitude but in time and space quadrature.Elliptical polar- The radiating elements each have av ization isaccomplished with a similar feed but with selective control of therelative amplitudes.

,In another form of the invention, like polarization efiects can beachieved through the use of traveling wave arrangements with radialwaveguides having similarly disposed radiating apertures. rangements,the feed means are disposed on the two plates defining the planesurfaces of the radial waveguide. These feed means mayconsist in oneformof a radial feed waveguide and a cylindrical waveguide, and inanother form of a pair of radial feed waveguides. The two structuresboth excite a pair of traveling wave modes within the radial waveguide,and selected relations between the input modes as to amplitude and phaseallows any type of polarization.

The novel features of this invention, as well as the invention itself,both as to its organization and method of operation, may best beunderstood when considered in the light of the following description,when taken in connection with the accompanying drawings, in which likereference numerals refer to like parts, and in which:

FIG. 1 is a perspective exploded view, partially in block diagram form,of a standing wave form of planar radial waveguide antenna capable ofoperating with arbitrarily selected polarization with a circularwaveguide feed in accordance with the invention;

FIG. 2 is a simplified perspective view showing an antenna such as thearrangement of FIG. I mounted flush with a surface of a supportingvehicle and providing a broadside pencil beam pattern (illustratedgenerally);

FIG. 3 is a plan view of theradial waveguide of FIG. 1, showingvectorial excitation components for the individual elements; 7

FIG. 4, including diagrammatic views FIGS. 4A, 4B

and 4C, shows plan views of the radial waveguide and sectional views ofthe circular feed waveguide, showing the correspondence between thedirection of polarization of energy in the feed waveguide andthe'radiation from the individual elements of the radial waveguide;

In the traveling wave ar- 7 J FIG. 5 is a simplified plan view of aradial waveguide and a section view of a circular waveguide of the formof FIG. 1, showing the manner in which circularly o'r ellipticallypolarized radiation can be provided;

' FIG. 6, comprising fragmentary plan views of radial waveguides similarto FIG; 1, shows diiferent configurations of an annular slot and themanner in which they r are arranged for the radiatingelements which maybe utilized to make up the total radiating aperture of the arrangementto reduce side lobes;

FIG. 7 is, an exploded perspective view of another form of antenna inaccordance with the invention, utilizing a radial waveguide antennaoperating with traveling wave excitation;

FIG. 11 is a fragmentary view'of the center. portion of the arrangementof FIG. 10, showing some of the features in greater detail; a

7 FIG. 12 is a sectional elevation View of the arrangement of FIGS. 10and ll, showing the exciting modes therein;

FIG.-l3 is a combined perspective and block diagram view of a systemconfiguration utilizing a conical scanning antenna in accordance withthe invention; and

FIG. 14 is a fragmentary sectional view of a part of the conicalscanning arrangement of FIG. 13.

Arrangements in accordance with the present invention are capable oftransmitting and receiving energy about the circle.

which can be arbitrarily polarized. The term arbitrarily polarized isintended to mean that'the antenna is capable of producing a patternwhich is independent of the direction of polarization and which, invarious forms, may be circularly or elliptically polarized as well aslinearly polarized in different directions. The term planar is intendedto indicate that the radiating surface of the antenna lies in' a givenplane, although the plane may be curved slightly to conform to theconfiguration of associated structures. Thus these antennas and thepatterns they provide are two-dimensional, and provide an additionaldegree of operational and design freedom over linear arrays. a

One arrangement in accordance with the invention for providing anarbitrarily polarized pattern is illustrated in exploded form in FIG. 1,and as installed in a flush surface in FIG. 2. As may be seen in FIG. 1,the antenna consists principally of a radial waveguide 10 having acentral axis and top and bottom plates 11 and 12 which are conductive,circular in form, and which lie substantially normal to the centralaxis. By referring to the top plate 11, it is not intended to indicatethat the antenna must be operated in a given position, but only thatthis is a normal frame of reference for the radial waveguide 10. The topplate 11, as may be seen in FIG..2, may be mounted flush with a surfaceof a streamlined vehicle 20, and may provide a pencil beam extendingsubstantially normal to the plane of the surface of the top plate 11.

V The top and bottom plates 11 and 12 are spaced apart a selecteddistance and joined at their outer periphery by a conductive ring 14which is affixed to both the plates 11 and 12. The bottom plate 12includes a central feed aperture 15 for exciting the radial waveguide 10with a desired mode. With the use of the outer conductive ring 14, theradial waveguide 10 is operated with standing waves. The radialwaveguide 10 is dimensioned to support the E mode. I r

The antenna aperture or composite radiating source of the radialwaveguide antenna 10 is formed by one or a number of what are heretermed annular slots. An annular slot is the convenient basic radiatingunit. of a radial waveguide. Each annular slot consists of a number ofindividual crossed slot elements 16 in the top plate 11. Although, as isdescribed'below, various shapes and dispositions can be employed for theradiating elements 16, the desired pattern can be achieved by thearrangement shown, in which the radiating elements 16 are disposed in anannulus or circle concentric with the central axis of the radialWaveguide 10. A number of the annular slots can be arrayed, as isdescribed in more detail below, to provide the total aperture of theantenna. Each of the crossed slots 16 has a like radial andcircumferential attitude with respect to the circle on which the slotslie, and the slots 16 are symmetrically placed about the top plate 11.The attitude of the slots 16 relative to an observer, however, varyprogressively Thus, the radiating elements are the crossed slots, whichtogether make up an annular slot.

The term annulus may be used to denote both a radiation aperture and ageometrical configuration.

The feed for this arrangement is intended to excite the radial waveguidein its E standing wave mode. The radial waveguide 10' is fed throughitscentral feed aperture 15 by a circular waveguide 17 coupled to thecentral aperture 15. An input source 19 is coupled to the circularwaveguide 17 and excites the circular waveguide 17 with input energy inthe TB mode which is the dominant circular waveguide mode. As isdescribed below, the polarization of the TE mode may be arbitrarilyvaried, and the circular waveguide 17 is particularly useful in thisrespect'because of its insensitivity to directions of polarization ofthe TE circular waveguide mode. It will be understood, however, that thedesired E mode'in the radial waveguide 10 may be established by otherfeed means. I

In the operation of the arrangement of FIG. 1, the input source 19excites the circular waveguide TE mode in the circular waveguide 17 (andan E mode is excited in the radial waveguide The standing wave E modewhich is established in the radial waveguide 10 provides current regionsin the top plate 11 which combine with the attitudes, configurations anddisposition of the radiating apertures 16 to provide controlledradiation patterns having the desired polarization characteristics. Theoperation of this antenna is reciprocal, in that currents which excitethe top plate 11 during reception of energy are provided as output in afashion which is the converse of the transmission operation. Theoperation is perhaps easier to visualize for transmission, however, andso will only be described in that context although the reciprocal naturewill be understood.

The E standing wave mode of a radial waveguide, such as the waveguide10, provides currents in the top plate 11 in both radial andcircumferential bands or regions. In accordance with the standing waveoperation established because of the presence of the conductive ring 14,the amplitude of these currents varies sinus'oidally at the frequency ofthe exciting source. At selected radii from the axis of the radialwaveguide 10, the amplitudes of the radial and circumferential currentscan be made equal. The currents are, however, displaced ninetyelectrical degrees. Thus with a standing wave operation the radial andcircumferential currents may be considered to be in phase quadrature,but having instantaneous total values which are equal. The magnitudes ofthe currents at the individual slots 16 vary at any instant dependentupon the position of the selected element 16.

The position of the radiating slots 16, the attitude of the radiatingslots 16, the equal amplitudes of the radial and circumferential currentregions and the quadrature relationship of the radial andcircumferential currents all contribute to the generation of selectivelypolarized wave energy with this planar array. The annulus of crossedslots 16 forms the aperture of the antenna. The radial position of thecrossed slots 16 with respect to the central axis of the radialWaveguide 10 corresponds to a point at which the amplitudes of the totalradial and circumferential currents at that radius are equal. Therelationship for the total current for any linear polarization may beexpressed as where I is the amplitude of the currents in the radial andcircumferential direction relative to the central axis of the radialwaveguide 10, as is the angular displacement of each slot from areference line on the planar surface, 6; and are direction unit vectors,and 'y is the angular displacement of the common plane of polarizationfrom the reference line. Each crossed slot 16, therefore intercepts aportion of the total current flowing and all the slots 16 together giverise to a radiated electromagnetic field having a common plane ofpolarization.

The resultant vectorial component of radiation from each individualcrossed slot 16 is the same. In other words, each crossed slot 16provides a radiation contribution to the antenna aperture pattern whichis of like magnitude and parallel to the same plane of polarization. Nocross polarization components are present. These facts may be betterunderstood by reference to FIG. 3, in which the excitation componentsfor the crossed slots 16 are shown in some detail. With the radial andcircumferential currents in a quadrature relation and assuming that thepolarization to be excited is in a vertical plane (taking a relativeposition of FIG. 3 as a frame of reference), then the uppermost slot 16(as seen in FIG. 3) is excited by a radial current but not by acircumferential current, the radial current being of full amplitude andthe circumferential current, ninety electrical degrees displacedtherefrom being zero. Proceeding clockwise around the crossed slots fromthe uppermost slot 16, however, the radial and circumferential currentsadd vectorially to a like resultant component at each individual slot16. This is due to the sinusoidal distribution of the two currents. Atthe ninety degree position (still proceeding clockwise from the top),the radial component is zero and the circumferential component amaximum, so that the resultant vectorial component of excitation at thiscrossed slot 16 is likewise equal in magnitude to the others andparallel to the same plane. The same result holds true for each of theother slot elements 16.

As may be seen in FIG. 4, the plane of polarization of radiated energyfrom the radial waveguide antenna 10 is dependent upon the polarizationof the TE mode in the feed waveguide 17. With reference to FIG. 4 only,we may speak of the angle 7 as relative to the vertical. Thus FIG. 4Ashows the relative position when the angle 7 for the feed energy and theexcitation is zero degrees, FIG. 4B shows the corresponding feed energyand radiated energy relationship when the angle 7 is 45 degrees and FIG.4C shows the like reiationships when the angle is ninety degrees.Although the displacement between the radial and circumferential currentregions remains the same, the distribution of the currents is shiftedangularly through desired values of 'y to achieve these results.

This arrangement may also be utilized to provide circularly orelliptically polarized energy. This result is accomplished in the mannerindicated generally in FIG. 5, in which FIG. 5A illustrates therelationship of the modes employed in the feed waveguide 17, and FIG. 53illustrates in simplified form the radiation resulting from excitationof the individual crossed slots 16.

Circularly polarized microwave energy may be con sidered as consistingof two linearly polarized components in time and space quadrature. Forcircularly polarized energy, the components are of equal amplitude andwhen the components are not of equal amplitude, the result iselliptically polarized energy. Accordingly, as shown in FIG. 5A, whenthe feed waveguide is excited with two orthogonally disposed TE modeswhich are of equal amplitude, but in time and space quadrature, arotating E mode is established in the radial waveguide 10.

As may be seen in FIG. 5A, one electric vector E may be used torepresent the electric field component of a first TE mode derived from afirst input source 21 coupled to the circular feed waveguide 17. Anotherelectric field vector E may be used to represent the correspondingcomponent of a second T5 mode derived from a second input source 22.Energy may be coupled into the circular waveguide 17 through appropriatetransition elements, apertures, or excitation elements, none of whichare shown but the use of which will be understood.

The sinusoidal variation of the individual vectors E and E with time maybe seen to provide a rotation of the resultant vector E of the feedenergy, due to the quadrature disposition of the individual vectors.Thus any rotating E mode excites the annular slot aperture of theantenna 10 to cause a rotation with time of the plane of polarization ofthe radiated electromagnetic waves. The relationship is such that thecommon plane of the radiation waves completes one full revolution in adistance equal to one free space Wavelength. Now by exciting the T13modes with unequal amplitudes (due to unequal electric vectors E and E arotating E mode is established which has an elliptical characteristic asa function or" time and which results in the radiation of ellipticalpolarization.

Antennas constructed in accordance with these principles are small insize, light and compact and easy to fabricate. They may be madearbitrarily thin and further may be flush mounted with a parallelsurface. Thus they can very simply provide functions heretofore suppliedonly by much more complicated structures.

In addition, however, these mechanical characteristics re accompanied byelectrical and operative characteristics which are significant. Theantenna is extremely easy to feed, and the polarization which'isradiated or detected may very readily be changed. Antennas conthisfashion inherently display low axial ratio when transmitting orreceiving circular polarization. They are two dimensional andconsequently, as is described more fully below, permit considerabledesign freedom in synthesizing and controlling radiation patterns.

Further features may also be employed where specific additionaladvantages are desired. Reference may be made, for example, to theshapes, radial dispositions and attitudes of the radiating elementsshown in the four different top plates illustrated in FlGS. 6A'through6D. As shown in FIG. 6A, the radiating elements 24 of an annular slotmay be made circular. Circular elements may be in some instances befabricated much more siniply than crossed slots, although each elementnonetheless may be excited with any polarization in the plane in whichthe annulus is located. The radiating elements alternatively, as shownin FIG. 68, may be constructed of crossed slots 25 whose individual armsare diagonally disposed with respect to the concentric annulus on whichthey lie. Again, these crossed slots 25 may be polarized in any desireddirection.

. Control of side lobes may be achieved by the arrangements illustratedin FIGS. 6C and 633, both of which utilize more than one concentricannulus of radiating elements. aninner annulus and slots 27 on an outerannulus which combine to form the'aperture of the antenna. As discussedpreviously, the requirement for each annulus is that it he on a radiusat which the radial and circumferential currents are equal in totalamplitude and separated by ninety electrical degrees (in For theselected excitation modes, this condition holds at discrete radii fromthe central axis. Accordingly, the contribution of each individualelement in an annular slot to the total radiation is the same in bothpolarity and magnitude. A modification of this technique, as shown inFIG. 6D, may employ an amplitude taper in the aperture by using annularslots which contain individual elements of different sizes and differentinterelement spacing. As seen therein, 'anantenna it of the typediscussed here may have an inner annulus of slots 31, a center annulusof slots 39, and an outer annulus of slots 29, the slots 29 of the outerannulus being smaller in size and further apart than the others. Bothvariations have been shown together but either could be used separately.Such arrangements provide additional degrees of freedom for theselective control of sidelobes.

The operating characteristics of. the arrangement thus provided shouldbe noted. ,The angular pattern is the same about the central axis,regardless of the type of polarization radiated. With the antennaoperating as a linearly polarized radiator there is no crosspolarization.

It will be recognized that'the excitation modes for the radialwaveguide'which can produce the desired current distributions are notconfined to the E mode mentioned. The standing wave modes whichhave thedesired characteristic are the E (where n=0, 1, 2 H (where P2 1, 2modes. The nomenclature adopted in designating these modes correspondsto that used in the Waveguide Handbook by N. Marcuvitz,

' McGriaw-Hill Press, p. 91 (1951).

Arbitrary control of the polarization of adiation pat- V terns can alsobe achieved by using traveling wave exc ted radial waveguide antennas.With these arrangements,

of the radial waveguide. The desired distributions are Thus, as in FIG.6C, there may be slots 26 on ...)andthe achieved through the use of aradial waveguide modal pair with one mode having a prescribed. relativephase and amplitude withrespect to the other.

An arrangement for providing traveling wave operation to achieveconstant shape pencil beams using any type of polarization is shown inFIGS. 7, 8 and 9, to which figures reference. is now made. A radialwaveguide antenna 40 having a top plate 41 and a bottom plate 42 may bearranged in the manner described with reference to the previous figures,and may have a central axis extending through the waveguide antenna 43in. a direction normal to the plane of the parallel plates 41 and 42.The waveguide antenna 40 may terminate in a circumferential band 43,but'is operated with the traveling wave modal pair through the presenceof a ring of resistive material 45 between the plates 41 and-42 at anouter radial portion of the antenna 40. The ring of resistive material45 may beany suitable microwave attenuating material and taperedinwardly with respect to the waveguide 40 so as to provide a smoothmatch for the microwave energy therein.

The top plate 41 of the radial waveguide antenna 40 may contain a numberof crossed slot elements 46 arranged in separate armuli'concentric withthe central axis of the radial waveguide-40. As in the arrangementspreviously described, the crossed slots 46 in the several .annuli aresymmetrically disposed within each of the annuli, and have like radialand circumferential attitudes with respect to the annulus on which theylie.

The structure by which the desired traveling wave modes are establishedwithin the radial waveguide antenna 4% consists in this arrangement of apair of feeds which are structurally. combined. Energy from a firstinput source 50 is coupled to a first circular waveguide 52 concentricwith the central axis of the radial waveguide 49 and, for purposes ofdescription, protruding through it from the bottom surface to beyond thetop plate 41. While the first circular waveguide '52 need not beconstructed as a unitary element extending entirely through the radialwaveguide 40, it will be more conveniently described as such'and the useof alternate methods of construction will be understood to be feasible.For coupling energy through-the bottom plate 42 of the radial waveguideantenna 4! the first circular waveguide 52 includes a number oflongitudinal slots '53 positioned on the side of the bottom wall 42parallel to the central axis and spaced apart from the bottom wall 42.For coupling energy supplied from the side of the top plate 41, thefirst circular waveguide includes a pair of annular slots 54, 55 insidethe radial waveguide antenna 40 and each adjacent inner surface of thebottom and top plate 42, 41 respectively. The first circular waveguide52 terminates in a short circuiting element 56 on the side ofthe topplate ll. A short circuiting element 57 is also positioned between theelongated slots 53 and the bottom plate 42. Thus the first circularwaveguide 52 is separatedinto one section which terminates short of thebottom plate 42 of the radial waveguide antenna 40, and another sectionwhich extends through the radial waveguide antenna 49 and'protrudes outthe top surface a short distance. The radial waveguide antenna 40, whichis the radiating structure of this arrangement, is to be distinguishedfrom a radial feed waveguide 60 coupled to and utilizing the bottomplate42 of the antenna 40. The radial feed waveguide '60 is concentric withthe central axis of the radial waveguide'antenna 40 and with the firstcircular waveguide 52 and includes as one of its parallel walls an innerradial portion of the bottom plate 42 of the radial waveguide 4t). Theradial feed waveguide 60 is electromagnetically coupled to the radialwaveguide antenna 40 through radially oriented coupling slots 61 whichare all positioned at a constant radius from the central axis of theradial waveguide 40. A rigid coaxial microwave transmission line 62 isformed by the outer surface of the first circular waveguide 52 and theinner surface of a second circular waveguide 63 registering with acentral opening in the radial waveguide feed 60 and concentricallyencompassing the first circular waveguide 52 for a distance pas-t thelongitudinal coupling slots 53. A variable coaxial short consisting of aconductive hollow cylinder 64 is utilized to control the length of therigid coaxial line 62, being concentric with'the central axis andmovable between the two circular waveguides 52, 63.

The portion of the first circular waveguide 52 which is inside theradial waveguide 40 may be supported by a ring 66 of material which issubstantially transparent to microwave energy. The ring 66 can includeinternal members which extend into the annular slots 54, 55 and whichprovide a precise axial spacing and dimensional control for the slots54, 55. The ring 66 may also be split for ease of assembly. The axialspacing of the annular slots 54, 55 forces the excitation of a desiredmode in the radial waveguide 40. Energy is fed into this portion of thefirst circular Waveguide 52 from a second input source 70 through acoaxial line 72 having an inner conductor which terminates as a firstprobe 73 inside the first circular waveguide 52 adjacent its end 56. Asecond probe 74 extending orthogonal to the first probe 73 may also beutilized to excite the first circular cylinder 52 in an additional mode.The second probe 74, and a coaxial feed line 75,..are shown only in FIG.8, and illustrate a feed which may be employed to excite any linear,either sense circular, or arbitrary elliptical polarization. With properfeed, therefore, the use of two orthogonal probes 73, 74 providesarbitrary polarization capability, although this immediate example hasfor simplicity been arranged only for linear polarization in FIGS. -7and 9.

In operation, considering linear polarization only, the arrangement ofFIGS. 7 through 9 operates by exciting the radial waveguide antenna 40concurrently in the E and H radial waveguide modes. When arranged tohave proper phase and amplitude relationships, as is described ingreater detail below, these modes excite the three annular slots eachcomposed of crossed slots 46 to provide a common plane of polarizationfor the radiated field at any given instant of time. The termination 45may be termed a flat load because it operates substantially withoutreflection. Means by which adjustments may be made in the direction ofpolarization have not been included in FIGS. 7 and 9, but it will beunderstood that the change in position of the polarization can beachieved through mechanical rotation of the feed elements relative tothe antenna or through electrical rotation of the energy. In addition,as discussed below, circular and elliptical polarization can be providedbecause of the feeds for the antenna basically consistof symmetricalmodes.

When operating with linearly polarized radiation, input energy is fed tothe opposite ends of the first circular waveguide 52 to excite the TEcircular waveguide mode therein, this energy being derived from thefirst input source 50 and a second input source 70. Specifically, thefirst input source 50 excites the TE mode in that side of the firstcircular waveguide 52 which is closest to it from the short circuitelement 57. The second input source 70 excites the other end of thefirst circular waveguide 52 through the probe 73 extending from thecoaxial line 72. The energy transfer thereafter may best be seen byreference to FIGURE 9.

Energy from the first input source 50 is utilizedto cause the forcedexcitation of an H radial waveguide mode in the radial waveguide antenna40. The longitudinal coupling slots 53 which extend axially along thefirst circular Waveguide couple energy into the region between the firstcircular waveguide 52 and the second circular waveguide 63. The rigidcoaxial line 62 defined by the two circular waveguides 52, 63 is excitedin a corresponding TE mode. Electric field distributions for the TE modein a rigid coaxial line correspond roughly to that of a circularwaveguide mode, except for the presence of the center conductor, so thatno transition elements are needed to in turn excite the E radialwaveguide mode. A variable coaxial short 64 is utilized to adjust theamplitude of the TE mode so that it delivers maximum energy to the Eradial waveguide mode.

Note that the symmetrical arrangement of the longitudinal slots 53 andof the remaining elements about the central axis permits any typepolarization to be excited in the direction normal to the central axis.Energy from the rigid coaxial line 62 couples directly into the radialfeed waveguide 66 to excite the E radial waveguide mode therein. As aresult, the radially disposed cou pling slots 61 in the bottom plate 42of the radial waveguide antenna 48' couple energy into the antenna 40,this energy being in the desired H radial waveguide mode.

Excitation of the radial waveguide antenna 46 in the second mode of themodal pair is also initiated by the establishment of a TE circularwaveguide mode in the portion of the first circular waveguide 52 whichincludes the segment passing through the radial waveguide antenna 40.The continuous annular slots 54, 55 concentric with the central axis andspaced 1/2 guide Wavelength apart couple out energy into the radialwaveguide antenna 40. Maximum coupling is achieved by positioning theshorting elements 56 and 57 at l/4 guide wavelength and 5/4 guidewavelength respectively from the probe 73 in the circular waveguide 52.

To establish a properly modal pair within the radial waveguide antenna40 there should in practice be some means of adjusting the amplitude andphase of the individual feed modes. An arrangement for providing controlof these parameters has not been shown in conjunction with FIGS. 7 to 9,for simplicity. One arrangement which might be used is however shown inFIG. 13. Other techniques will also suggest themselves to' those skilledin the art.

Thus, by this control the E and H radial waveguide modes are establishedwithin the radial waveguide antenna 40, and because absorptivetermination of the energy in the resistive termination 45 causestraveling wave operation, the desired current distributions are presentover the entire top plate 41. So for the three annular slot aperture theradial and circumferential currents exciting them again produce aradiated field which has a common plane of polarization at any giveninstant of time.

A desired modal pair may also be established by the use of a difierentfeed arrangement, such as that illustrated in FIGS. 10 through 12 andhaving like numbers for some of the like parts. As shown therein, aradial Waveguide antenna 40 may have top and bottom plates 41, 42disposed about a central axis, with an internal ring of resistivematerial forming a flat load 45 within an outer circumferential band 43.In the same manner as the arrangement of FIGS. 7 through 9, crossedslots 46 may be disposed in annuli concentric with the central axis, thecrossed slots 75 being symmetrically placed with respect to thecircumference on which they lie. is arrangement may utilize a firstcircular waveguide connected to the bottom plate 42 of the radialwaveguide antenna 40 and a second circular waveguide 81 connected to thetop plate 41 of the radial waveguide antenna 46. Each of the circularwaveguides 8t and 81 may register with a corresponding opening in theassociated Wall or plate, 42 or 41 respectively, of the antenna 40. Asource (not shown) may be coupled to first circular waveguide 80 forexciting the TE circular waveguide mode, and a separate source (also notshown) may be coupled through a first coaxial line 83 having a centerconductor terminating as a probe 84 Within the second circular waveguide81. To establish circular or elliptical polarization .a separate probe85 coupled to order to propagate the E another coaxial feed line may bemounted in a direction orthogonal to the probe 84 extending from thefirst coaxiail line 83. The circular waveguides 80, 81 are thus alike asto the modes which each indirectly provides to the radial waveguideantenna 40. An end plate 86 terminates the second circular waveguide 81.

Each of the circular waveguides 80 and 81 is coupled to a dilferent oneof first and secondradial waveguide feeds 90, 94 respectively. These'mayalso be referred to as radial feed waveguides. Radial waveguide feeds90, 94 each include a different circular plate 91 and 95 respectively,which is connected by an outer flange 92 and 96 to an inner radialportion of the bottom wall and top Wall 42 and 41 respectively of theradial waveguide antenna 49. The first radial waveguide feed 90 includesa number of crossed slots 23 disposed inan annulus concentric with thecentral axis of the waveguide antenna 4% and each having a radial andcircumferential arm with respect tothe central axis and the annulus uponwhichit lies. In likefashion, the second radial waveguide feed94 hascrossed slots 97 identically shaped and spaced. A pair or tapered outerrings 98, 99' around the outer periphery of the flanges of the tworadial feed waveguides 9t 94 provides a smooth transition for microwaveenergy between the waveguide feeds 90, 94

y and the associated radial waveguide antenna 40.

In operation, the arrangement thus provided together with externalcontrols such as phase shifters and attenuators in both inputsforces thedependent excitation of the desired E and H radial waveguide modes andwith the prescribed relative phase and amplitude in the radial waveguideantenna 49. As may be seen best in FIG.

, 12, the TE mode in the first circular waveguide 80 eshalf the requiredcurrent distribution necessary to propagate the E and H radialwaveguidemodal pair. Concurrentl', the TE mode'excited in the second circularwaveguide 81 by the energy in the coaxial line 83 excites an E radialwaveguide mode in the second radial feed 7 waveguide 94. This mode inturn provides, through its crossed slots 97 in the second radialwaveguide feed 94,

the other half of the required current distribution on the lower plate4-2 of the radial Waveguide antenna 40, in V and H radial waveguidemodal pair.

Again, therefore, the desired modal pair of traveling 'wave modes isestablished within the radial Waveguide antenna 40. Consequently, theradial and circumferential currents at each of the crossed slots 46,composing the three annular slots, provide at any instant of time aradiated field which is polarized parallel to a common plane ofpolarization.

Both these traveling wave anrangements'thus operate by properly fixingthe amplitude and phase of the two traveling wave modes which are beingexcited in the-radial waveguide antenna 40. Each establishes the desiredcurout of phase, and with the prescribed relative amplitude as shown inthe next equation a where A and B are the real amplitudes of the E andId radial waveguide modes respectively, b is theheight of the annulican'be disposed at smaller'radii 12 radial waveguide, and g is theintrinsic admittance. Having this desired relative phase and amplitude,the radial waveguide modal pair produces a total current flowing overthe entire aperture plate that has the form,

It= p[ 0 1 Sill ()l+ 0 1p) cos where and 6,, are unit vectors in theradial and circumferential directions respectively. The radialdependence of the two orthogonal currents is thus determined bythe sameexpression H (K p), which is a Hankel function of order zero, where Thusunder these conditions the radial and circumferential currents of thetraveling wave device everywhere have the desired relationships, and'theannuli need not be placed at any specific radii. With the traveling wavedevice there is no limitation on the number of annuli which The totalaperture or source of the antenna consequently can be focused by controlof phasing. Additionally, amplitude control can be obtained by selectivealteration 'of the size and the interelement spacing of the individualcrossed slots in the successive annular arrangements. In this respect,it should be noted that there is usually an inherent amplitude taper inthe traveling wave arrays, due to the Hankel function dependence of theoutward traveling wave model pair. 7 y

Traveling wave arrays therefore have a number of significant operatingfeatures and excellent versatility.

For a given size aperture, they have greater aperture emciency. Theyalso have wide bandwidth. For many applications where low sidelobes areof extreme importance, their arraying potential gives them particularattractiveness.

The, examples shown are merely to illustrate the arrangement ofstructures in accordance with the invention and it will be understoodthat other variations are possible. As with the standing Wave array, thetraveling Wave radial waveguide antenna may provide linear polarizationof any direction, circular polarization of either sense of rotation, orelliptical polarization. Two'mod'al pairs are employed for suchpolarization characteristics. It may be seen in' the arrangements of'FIGS.'8, l0 and 11, that the crossed probes 73, '74 (FIG. 8) and 84, 85(FIGS. 10 and 11) may be utilized to provide such dual excitation. Itwill also be understood that the E and H modal pair is illustrative ofonly one specific relationship in a general class of relationships whichmay be employed. In the general case, the E and H modal pairs can beused, wheren=l,2,3.. V

A number of other arrangements will also suggest themselves to thoseskilled in the art. Where it is desired to have a .much more compacttraveling wave arrangement, for example, the tapered flat load shown inthe two travel ing wave arrangements can be replaced by a more compact'termination. Additionally, the central feed structure can be made morecompact, if desired, so that the It will also be recognized that themodal pair can be excited without utilizing a protruding feed; Theentire ,feed may be accomplished from one's'ide of the radial waveguide,so that the structure would be completely flush'with an associated It isnonetheless apparent that the small promajority of circumstances.

There is illustrated, in FIGS. 13 and 14, another arrangement showingthe manner in which a radial waveguide antenna 100 may be employed in asystem context. These figures provide an exemplification of a conicalscanning arrangement and are also illustrative of the manner in whichdesired modes can be established and controlled as to amplitude andphase. Other arrangements will suggest themselves to those skilled inthe art, but the provision of this specific example will assist inmaking the arrangement clear.

The antenna 100 itself is best seen in FIG. 14. It is intended tooperate as a standing wave device, and has one annulus consisting of anumber of crossed slots 101, only a few of which have been illustratedfor simplicity. The antenna 100 is fed by a circular waveguide 103 whichis coupled to an opening in the central axis of the waveguide 100 in themanner prew'ously described. The waveguide 100 also includes an internaldielectric member 102 which is eccentrically placed with respect to thecentral axis of the antenna 100. The dielectric member 102 acts as aphase shifter within the radial waveguide antenna 100, and serves toslow waves therein to an extent determined by the amount of dielectricin the radial path. The shape of the dielectric member 102 is not acircle, but is varied in accordance with functions apparent to thoseskilled in antenna synthesis to provide a desired phase variation at theindividual elements of the aperture. The net result is that the antennapattern is tilted slightly off the central axis of the antenna 100. Thetilting is in the direction opposite to the greatest radial displacementof the dielectric member 102 from the central axis. If, therefore, theantenna 100 can be rotated about its central axis, a conical scanningarrangement will be provided.

As seen in FIG. 13, this antenna may be mounted flush with an associatedsurface 105, and may contain a peripheral gear 106 which is driven by anassociated gear 107 which is in turn rotated by a motor 108. The motor108 may rotate the antenna 100 continuously, or may provide incrementalangular positions.

The arrangement shown for exciting the antenna 100 provides a generalillustration of the manner in which amplitude and phase control may beprovided in the other arrangements previously discussed. A source ofenergy 109 provides microwave energy into two different channels. Onechannel contains a first variable phase shifter 110 and a first variableattenuator 114, and the other channel contains a second variable phaseshifter 111 and a second variable attenuator 115. The outputs from thetwo variable attenuators 114 and 115 may constitute a pair oforthogonally disposed probes 117 and 118 in a circular waveguide section119. This circular waveguide section is coupled to the circularwaveguide feed 103 of the antenna 100 through a microwave rotary joint120. e The arrangement thus provided illustrates both conical scanningand the control of excitation of the antenna 100 through amplitude andphase adjustments. The antenna 100 provides its olf-axis beam duringrotation by the motor 108, for conical scanning. The symmetricalarrangement of the feed waveguide 103 and the coupled rotary joint 120is independent of the direction of polarization of the radiation coupledto the antenna 100. The orthogonally disposed probes 117, 118, however,can establish direction of linear polarization, circular polarization ofeither sense of rotation, or elliptical polarization in the associatedwaveguide 119. Such variations are effected by the two variable phaseshifters 110, 111 and the two variable attenuators 114, 115. Theattenuators 114, 115 determine amplitude, and the phase shifters 110,111 determine the phase of the excitation modes. For a rotatingpolarization, the phase shifters would be operated cyclically.

The scanning antenna thus provided is substantially mechanicallysymmetrical and thus is largely free of inertial effects. This fact incombination with the substantially planar structure make it possible touse the antenna 100 in a forward part of a lightweight and streamlinedsystem without complicating balance and weight distnibution problems.Conical scanning might also be achieved through the use of a thinstanding wave arrangement which is slightly tilted with respect to thecentral axis, or which has a slight bend in the feed waveguide. Sucharrangement can be made arbitrarily thin and extremely small.

Thus there has been provided a new family of planar surfaced antennashaving arbitrary polarization capabilities and providing broadsidepencil beams. Antennas constructed in accordance with this invention arecompact, lightweight and have versatile operating characteristics.

We claim 1. A planar surfaced antenna capable of operating with likepatterns independently of the polarization characteristic of theradiation being transduced, the antenna comprising: a radial waveguidehaving parallel conductive plates, one of the plates including at leastone annular aperture defined by a number of crossed slots arranged on anannulus disposed about the center of the radial waveguide, the crossedslots having like radial and circumferential attitudes with respect tothe annulus on which they lie; and means coupled to the radial waveguideat the central axis thereof for exciting the radial waveguide surfacecontaining the crossed slots with radial and circumferential currentcomponents which are equal in amplitude at the annulus containing thecrossed slots and which are displaced from one another by ninetyelectrical degrees.

2. An arbitrarily polarized planar antenna array comprising a radialwaveguide having an antenna aperture defined by a plurality ofindividual radiating elements disposed concentrically about the centerof the radial wavequide in one surface thereof, the radiating elementscomprisin individual apertures shaped to provide radiation components inany direction in the plane of the surface in which they are positioned;and wave energy feed means coupled to the radial waveguide at thecentral axis thereof and energizing the radial waveguide in at least oneradial waveguide mode for establishing radial and circumferentialcurrents in the surface thereof containing the radiating elements, theposition of the radiating elements being selected such that the totalvectorial radiation component at each aperture is like that at theothers in magnitude and direction.

3. An antenna comprising: a conductive surface plate providing aradiating source defined by a number of individual radiating elementsdisposed on an annulus about a center point, the radiating elementsbeing of a form having equal radial and circuferential excitationcapabilities with reference to the center point; and meanselectromagnetically coupled to the surface plate for exciting theradiating elements with radial and circumferential currents thereatwhich are equal in total amplitude at the annulus but relativelydisplaced at the individual elements so that the resultant vector ofradiation provided at each element is caused, by the attitude of eachindividual radiating element and the current excitation thereat, toprovide like resultant components from each of the radiating elements.

4. An antenna having a planar radiating surface and being capable ofbeing mounted flush with a supporting structure, the antenna providing apencil beam pattern of a substantially like characteristic independentlyof the polarization characteristics of the radiation which is transducedby the antenna and comprising: a radial waveguide having a central axisand defined by a pair of parallel conductive plates, one of the platescontaining a plurality of crossed slots which together define an annularantenna aperture, the crossed slots being disposed in circles about thecentral axis of the radial waveguide and the circles lying at selectedradial distances from the central axis, the crossed slots beingsymmetrically placed about and having like attitudes with respect to thecircles on which they lie; termination means positioned between 7 guidehaving parallel conductive plates and a central axis extending normal tothe plates, one of the plates having a number of crossed slots therein,the slots lying in at least one annulus about the central axis andhaving sea lectediattitudes and positions; wave'encrgy termination meanscoupled between the plates at a radius further from the central axisthan the crossed slots; and means coupled to the radial waveguide forexciting modes therein which establish at least two current regions inthe platecontaining the crossed slots, the current regions and theattitudes and positions of the crossed slots combining to provideuniform operation independent of the direction of excitation of thecrossed slots.

6. A planar antenna for providing a broadside pencil beam pattern andfor operating substantially independently of polarizationcharacteristics, the antenna comprising: a radial waveguide including apair of parallel conductive plates and a circumferential conductive bandfor providing standing wave operation, one of the plates having at leastone annular radiating aperturedefined by a number of crossed slots oflike configuration disposed symmetrically on at least one annulus aboutthe center of the radial waveguide, each of the crossed slots having alike radial and circumferential attitude with respect to the annulus onwhich it lies; and wave energy feed means coupled to one of the platesof the radial Waveguide at the center thereof for providing coupling toa selected radial waveguide mode in which radial and circumferentialcurrents of equal amplitude but ninetydegree relative displacement areprovided at the annuli containing the crossed slots, such that theexcitations of each of the'crossed slots are like in amplitude anddirection.

waveguide having a number of radiating elements symmetrically placedabout a selected point in the Waveguide, the elements havingnonpolarization sensitive configurations; and means at the selectedpoint in the waveguide for coupling energy thereto which providesexcitation of the individual elements with orthogonally disposedcomponents. i

8. An antenna comprising: a radial waveguide includaxis and encompassingthe plate and a radiating surface plate coupled to the terminatingflange and being substantially parallel'to the first plate, theradiating surface plate including a plurality of crossed slots disposedin at least one annulus concentric with the axis' of the radialwaveguide, the crossed slots having like angular positions with respectto the annulus on which they lie; and means coupled to the first plateof the radial waveguide for feeding Wave energy thereto to establishradial and circumferential currents of "90 phase disposition at each ofthe crossed slots in the radiating plate.

7. An antenna comprising: a standing wave radial sing a first plateconcentrically positioned about a central c axis, a conductiveterminating flange concentric with the 9. An antenna for providing acircularly or elliptically' polarized pencil beam pattern broadside to aplanar surface and comprising: astanding wave radial waveguide havingparallel'top and bottom plates, the top plate having a total antennaaperture defined by at least one annular slot consisting of a circulararrangement of crossed slots disposed concentrically about the center ofthe radial waveguide, the crossed slots each having like radial andcircumferential attitudes with respect to the center of theradialwaveguide, the radial waveguide being dimensioned to support the Emode; a circular-feed waveguide coupled to the radial Waveguide; meanscoupled to the feed waveguide for exciting a first TE mode therein, sothat a first E mode is excited in the radial waveguide to excite thecrossed slots with radial and circumferential currents which are equalin amplitude but displaced by ninety electrical degrees to provide afirst like instantaneous ,vectorial component at each crossed slot; andmeans coupled to the feed waveguide for exciting a second TE modetherein which'is orthogonal with respect to the first TE mode and has aselected amplitude relationship, the second TE mode exciting. a second Emode in the radial waveguide which is in quadrature with the first Emode, so that secondlike instantaneous vectorial'components are providedat each annular slot, the two instantaneous vectorial components varyingwith time to providea total rotating electromagnetic wave energycomponent having a degree of el-lipticity determined by the relativemagnitudes of the exciting modes.

10. A planar antenna for transducing between a confined energy mode andarbitrarily polarized space radiation, said antenna comprising: a radialwaveguide including a first circular conductive plate'concentric with agiven axis, a short circuiting conductive band about the firstconductive plate and fixed thereto, and a secondconductive plateparallel to and coextensive with the first con ductive plate, andattached to the conductive band to define with the first conductiveplate a radial waveguide dimensioned to support the E standing wave modeof a radial waveguide, the second conductive plate having at least oneannulus of crossed slots disposed concentrically about the axis atsymmetrically spaced radial positions, the crossed slots defining anannular aperture and having like relative positions with respect to theannulus on which they lie, thefirst conductive plate having a centralfeed aperture; a circular waveguide coupled to the central feed apertureof the first conductive plate of the radial waveguide and concentricwith the axis thereof; and means for exciting the circular waveguide inthe dominant TE mode of a circular waveguide for establishing the Estanding wave mode in the radial waveguide.

11. An antenna comprising: a radial waveguide having top and bottomconductive plates, the top plate having at least, one'group of radiatingapertures each having a crossed slot configuration and lying in an innerregion of the radialwaveguide; termination means positioncd'between thetop and bottom plates in an outer region of the radial waveguide andthereby providing a traveling wave array; first means coupled to thebottom plate of the radial Waveguide for exciting therein a firsttraveling wave mode; and second means coupled to the top plate of theradial Waveguide for exciting therein a second traveling wave modehaving selected amplitude and phase relationships With respect to thefirst traveling wave model 12. An antenna comprising: a radial waveguideantenna'having a number of radiating elements in one wall thereof spacedfrom the center of the radial waveguide, each of the apertures beingexcitable in both radial and circumferential directions relative to theradial waveguide antenna; feed means coupled to the radial waveguideantenna at the center thereof for exciting therein a pair of modeshaving selected phase and amplitude relationships; and dissipativetermination means within the, radial waveguide adjacent the peripherythereof for operating the radialwaveguide antenna in a traveling wavemode.

13. A radial Waveguide antenna for providing a pencil beam patternandoperating substantially independently of the polarizationcharacteristics of the radiated wave, said antenna comprising: a radialwaveguide having a plurality of crossed slots in one wall, the slotshaving like attitudes relative to'the central axis of the radialwaveguide;

exciting the radial waveguide in a pair of traveling wavemodes providingequal total current amplitudes and hav- 1 7 ing a selected phaseseparation, such that the excitation of each of the crossed slots isequal in magnitude and parallel to a selected plane.

14. A planar antenna array for providing an arbitrary polarizationpattern and comprising: a radial waveguide antenna defined by a pair ofparallel "plates concentric with a central axis, the radial waveguideantenna including a plurality of radiating elements having aconfiguration such that they may be excited in any direction in theplane of the surface in which they lie; means coupled to at least one ofthe plates for exciting the radial waveguide antenna in an E mode, wheren=0, 1, 2'. and means coupled to the other of the plates of the radialwaveguide antenna for exciting the radial waveguide antenna in an Hmode, where n=0, 1, 2 the two modes being separated by and arranged toprovide relatively equal total current amplitude.

15. An antenna comprising: a radial waveguide antenna arranged tooperate in a traveling wave mode and having a plurality of crossed slotsin a first wall thereof and disposed symmetrically about the centralaxis of the radial waveguide; a centrally disposed circular waveguidecoupled to the radial waveguide along the central axis thereof andprotruding through both walls of the radial waveguide, the firstcircular waveguide including annular slots within the radial waveguidefor exciting a selected mode within the radial waveguide antenna, andlongitudinal slots in the side which protudes from the second wall;means coupled to the first circular waveguide adjacent the first wall ofthe radial waveguide for feeding waves of desired amplitude and phase tothe circular waveguide, thereby to excite the radial waveguide in a modeof selected amplitude and phase through the annular slots; 2 secondcircular waveguide encompassing the first circular waveguide at theprotruding portion which extends 'from the second wall of the radialwaveguide and being coupled thereto by the longitudinal slots in thefirst circular waveguide and forming therewith a coaxial waveguide; aradial feed waveguide coupled to the coaxial waveguide and to the secondwall of the radial waveguide antenna and electromagnetically coupled byradially oriented slots therein to the interior of the radial waveguideantenna; and means coupled to the portion of the first circularwaveguide which protrudes from the second wall of the radial waveguideantenna for exciting the first circular waveguide in a selected mode, sothat energy in the first circular waveguide excites the coaxialwaveguide and in turn the radial feed waveguide so that a second mode ofselected characteristics is established in the radial waveguide antenna.

16. An antenna for providing a pencil beam broadside to a substantiallyplanar surface, the antenna operating substantially independently of thepolarization characteristics of the space propagated wave upon which itoperates and comprising: a radial waveguide antenna having top andbottom conductive plates disposed about a central axis normal to theplates, the top plate including a plurality of crossed slots disposed inconcentric annuli about the central axis, the crossed slots in each ofthe annuli being symmetrically disposed and having like radial andcircumferential attitudes with respect to the annulus on which they lie,the bottom plate including radially oriented slots disposedsymmetrically about the central axis of the radial waveguide at an innerradius thereof; a ring of resistive material disposed between the topand bottom plates of the radial waveguide and at a further radius fromthe central axis than the outermost annulus of crossed slots, the ringof resistive material having a taper of increasing height in the outwarddirection so as to provide traveling wave operation of the radialwaveguide antenna; a radial feed waveguide coupled to the bottom plateof the radial waveguide and electromagnetically coupled to the radiallyoriented slots therein; a first circular waveguide concentric with thecentral axis and coupled to the radial feed waveguide to form the outerconductor of a rigid coaxial line; a second circular waveguide extendingthrough the first circular waveguide and through the radial waveguidefrom the bottom plate side to the top plate side and terminating at thetop plate side; the second circular waveguide including a ring oflongitudinal slots which are elongated in the direction of the centralaxis and further disposed from the radial waveguide than the radial feedwaveguide and within the length of the first circular waveguide, thesecond circular waveguide also including annular circumferential slotsadjacent the inner surfaces of the top plate and the bottom plate withinthe radial waveguide antenna; a conductive short circuiting elementextending across the interior of the second circular waveguide betweenthe radial waveguide and the longitudinal slots in the second circularwaveguide; feed means coupled to the portion of the second circularwaveguide protruding beyond the top plate of the radial waveguide; feedmeans coupled to the second circular waveguide on the bottom plate sidethereof; and a cylindrical coaxial shorting member movably positionedbetween the outer surface of the second circular waveguide and the innersurface of the first circular waveguide for controlling the length ofthe rigid coaxial transmission line extending along the two circularwaveguides in a direction away from the radial waveguide and the radialfeed waveguide.

17. An antenna comprising: a radial waveguide antenna arranged tooperate in a traveling wave mode having a pair of walls, a first ofwhich includes a plurality of crossed slot apertures; means including afirst radial feed waveguide coupled to the first wall for exciting afirst radial waveguide mode in the radial waveguide antenna; and meansincluding a second radial feed waveguide coupled to the second wall ofthe radial Waveguide antenna for exciting a second radial waveguide modetherein, the two radial waveguide modes having a selected phaseseparation and having equal total current amplitudes.

18. A planar-surfaced antenna capable of providing a pencil beam patternbroadside to the planar surface and substantially independent incharacteristics of the nature and direction of the polarization uponwhich the antenna operates, the antenna comprising: a radial waveguideantenna structure comprising a pair of conductive plates parallel toeach other and symmetrically disposed about a central axis, a first ofthe plates providing the planar surface of the antenna and includingcrossed slot radiating apertures therein, the apertures being disposedin symmetric fashion in annuli concentric with the central axis, thecrossed slots having like radial and circumferential attitudes withrespect to the annulus upon which they lie; a terminating load ringpositioned between the plates of the radial waveguide at an outer radiusthereof and providing traveling wave operation of the radial waveguide;a first circular waveguide coupled to the outer surface of the firstplate at the central axis; a first radial feed waveguide coupled to andcompleted by the inner surface of the first plate of the radialwaveguide antenna and concentric with the central axis, the first radialfeed waveguide being fed by the first circular waveguide and including aplurality of crossed slots disposed in its innermost surface in a feedannulus concentric with the central axis; a second circular waveguidecoupled to the second plate of the radial antenna waveguide at the outersurface thereof; a second radial feed waveguide coupled to and completedby the inner surface of the second plate of the radial antenna waveguideand including a plurality of crossed slots disposed in a feed annulusabout the central axis; means coupled to the first circular waveguidefor exciting the first circular waveguide in a TE mode,

thereby to excite the E radial waveguide mode inthe V first radial feedwaveguide for establishing an E radial waveguide mode in the radialantenna Waveguide; and

means coupled to the second circular waveguide for exciting "the secondcircular waveguide in a TE mode to establish an E radial waveguide modein the second radial feed Waveguide, thereby to excite the radialwaveguide antenna in an H radial waveguide mode, the

:20 means for exciting the circular waveguides being an ranged toprovide a selected phase-difierence between the E and H modes in theradial waveguide-antenna, and

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3322506 February 20, 1962 Frank J. Goebels, Jr, v at a1;

It is hereby certified that error appears in the above numbered patenl'.requiring correction and that the said Letters Patent should read ascorrected below.

Column 1, line 57 for "objected" read object column 2 line 47 for"circlt" read circle column 7, line l9 strike out "'be" first,occurrence; column 9 line 53 strike out "of" first occurrence; column lllines 2 and 3 for "coaxiaiP' read m coaxial column 12, line 13 to 14 forthat portion 01' the equation reading read W b b Column line 51, for"circuferential" read circumferential --o Signed and sealed this 28thday of August 1962 (SEAL) Attest;

ESTON G; JOHNSON DAVID L LAUU Atltesting Officer Commiesioner of Patents

